1. Optical coherence tomography (OCT) uses light interferometry to perform high-resolution, cross-sectional imaging of the retina. It provides quantitative measurements of retinal nerve fiber layer thickness. 2. OCT images are analyzed to detect structural changes in the optic nerve head and retinal nerve fiber layer that can indicate glaucoma, often before visual field defects appear. Parameters like retinal nerve fiber layer thickness, cup-to-disc ratio, and nerve fiber layer deviation maps are used to diagnose and monitor glaucoma progression. 3. Macular ganglion cell complex thickness, which includes the retinal nerve fiber layer, ganglion cell layer, and inner plexiform layer, can also detect early glaucomatous loss

1. OCT in Glaucoma
LT. COL. RASHED-UL-HASAN
FELLOW TRAINEE (GLAUCOMA)

2. Various imaging techniques
Anterior Segment:
AS-OCT
UBM
Posterior Segment:
OCT
HRT
GDx
ONH imaging

3. Quantitative Imaging
Principles Clinical Parameters
Measured
OCT Interferometry Retinal Nerve Fiber Layer
Thickness
HRT Confocal Scanning Laser
Ophthalmoscopy
Optic Disc Tomography
GDx Scanning Laser
Polarimetry
Retinal Nerve Fiber Layer
Thickness

4. Structural damage precede functional loss
About 50% of RNFL has to be lost*
Window ofabout 6 years
Dr. Harry Quigley. Kerrigan- Baummen, Quigley et al. IOVS 2000

5. OPTICAL COHERENCE TOMOGRAPHY
(OCT)

6.  New diagnostic imaging tool
 Non invasive, real-time, high resolution
 Principle – light interferometry
 Uses low coherence light in the near-infrared range (820nm)
to perform cross-sectional images of biological tissues
 Axial resolution – 10µ
 Transverse resolution – 20µ
INTRODUCTION

7. Optical
Coherance
Tomography
Normal scan:
Very unlikely
there is
glaucoma
8
Physiological
cupping from
early glaucoma
Diagnose and follow up
pre perimetric glaucoma
Monitor
progression
confirm whether
VF defect is real
or an artifact

8. Various OCT instruments are available
- Zeiss
- Topcon
- Optovue
- Heidelberg
- Nadik
9

9. PRINCIPLE OF OCT
 Near infra-red beam (820 nm) split
into two components:
Probe beam: To the tissue of interest
(retina)
Reference beam: Travels to a
reference mirror at a known variable
position

10. PRINCIPLE OF OCT
 Light reflected back from the
boundaries of the microstructures
 Echo time delay of this light (reflected
from the retina) is compared with the
same of the reference mirror and the
interference pattern is noted

11. PRINCIPLE OF OCT
 Interference measured by a
photodetector
 Real time tomogram using a false
colour scale

12. PRINCIPLE OF OCT

13. Types of OCT
OCT
TIME DOMAIN OCT FOURIER DOMAIN OCT
SPECTRAL DOMAIN (SD) OCT SWEPT SOURCE (SS) OCT

14. TIME DOMAIN OCT FOURIER DOMAIN OCT
A scans generated sequentially one
pixel at a time in depth
Entire A scan generated at once based
on Fourier transformation of
spectrometer analysis
Moving reference mirror Stationary reference mirror
400 A scans per second 26000 A scans per second
10 micron depth resolution 5 micron depth resolution
B scan (512 A scans) in 1.28 seconds B scan (1024 A scans) in 0.04 seconds
Slower than eye movement Faster than eye movement

16. TIME DOMAIN OCT
SLD
Detector
DataAcquisition
Processing
Combines light
from reference
with reflected
lightfrom retina
Distancedetermines
depth in Ascan
Reference mirror moves
back andforth
Lens
Scanningmirror
directs SLD
beam onretina
Interferometer
Broadband
LightSource
Creates A-
scan 1 pixel at
a time
FinalA-scan
Process
repeated many
times tocreate
B-scan

17. FOURIER DOMAIN OCT
SLD
Spectrometer
analyzes signal
bywavelength
FFT
Gratingsplits
signal by
wavelength
Broadband
LightSource
Combines light
from reference
with reflected
light fromretina
Interferometer
Spectral
interferogram
Fouriertransform
converts signal to
typical A-scan
EntireA-scan
created at a
singletime
Process
repeated many
times tocreate
B-scan
Referencemirror
stationary

18.  SD-OCT use
 Broadband near-infrared superluminescent diode , SLD (840 nm) as a
light source
 Spectrometer as the detector
 SS-OCT use
 Tunable swept laser of 1050 nm
 Single photodiode detector
SD OCT & SS OCT

19. • Optic nerve head (ONH)
• Peripapillary retinal nerve fibre
layer (RNFL)
• Macular ganglion cell complex
(GCC)
• 03 innermost layer of retina
(RNFL+ GCL+ IPL)
ANALYSIS FROM OCT

20. RNFL ANALYSIS
 RNFL analysis helps to
identify early glaucomatous
loss
 Circular scans of 3.4 mm diameter in
the peripapillary region (cylindrical
retinal cross-section)
 Itisgraphed in a TSNIT orientation
 Compared to age-matched
normative data

21. OPTIC NERVE HEAD ANALYSIS
• Radial line scans through optic disc
provide cross-sectional information on
cupping and neuroretinal rim area
• Disc margins are objectively identified
using signal from "End of RPE (BMO)”
• Parameters:
• Disc
• cup and rim area
• horizontal and vertical cup-to-disc ratio
• vertical integrated rim area
• horizontal integrated rim width

22. INTERPRETATION
OF
OCT

23. COLOUR CODE
 Colour Code A : RNFL thickness map
 Warm colour (yellow, red) : Thicker
 Cold colour (blue, green): Thinner
 Colour Code B:
 All other zone other than 8 & 9
 Compared to age-matched normative data
 Colour Code C : zone 8 & 9
 False colour code based on tissue
reflectance
 Warm colour (yellow, red) : High reflectance
 Cold colour (blue, green): Low reflectance

24. ZONES OF OCT
Zone-1 : Pt. I.D & Signal strength
Zone-2 : Key parameter table
Zone-3 : RNFL thickness map
Zone-4 : NRR thickness plot
Zone-5 : RNFL deviation map
Zone-6 : RNFL thickness TSNIT PLOT
Zone-7 : RNFL Quadrant & RNFL Clock-hour
thickness measurement
Zone-8 : Extracted vertical & horizontal
tomogram
Zone-9 : RNFL circular tomogram

25. Zone-1. SIGNALSTRENGTH
• Determines the reliability
• Cirrus OCT: >/= 6/10
• Optovue: 40 and above

26. Zone-1. SIGNALSTRENGTH
• Poor signal strength causes
• Media opacities
• Dry eye
• Fixation inability
• Poor OCT lens cleaning
• Older device
• Poor centration
• Inexperienced operator

27. Zone-2 : Key parameter table
 Results are compared with normative
database values & colour coded
according to distribution

28.  Normal – hour-glass or butterfly
wing appearance, yellow and red
 Only map without any relation with
normative database
 Abnormal –
1. Asymmetry between superior and
inferior sectors
2. Early signs of a peripheral defect -
blue notch in yellow red sectors
Zone - 3 : RNFLTHICKNESS MAP

29. RE– Continuous line
LE – Dotted lines
Normal zones - Green
Abnormal zones - Yellow and red
Zone - 4 : NRR THICKNESS PLOT

30. Enface infrared image
3.46 mm in diameter, used as a
reference zone for evaluation of
RNFL thickness.
Outside normal limits – yellow and
red
Zone - 5 : RNFLDEVIATION MAP

31. HEALTHY GLAUCOMA SUSPECT MODERATE GLAUCOMA SEVERE GLAUCOMA

32. Thickness of the RNFL in different
regions ( TSNIT : temporal, superior,
nasal, inferior, temporal) at 3.4 mm
from centre of the optic nerve
Normal zones - Green
Abnormal zones - Yellow and red
Zone - 6 : RNFLTHICKNESS
TSNIT PLOT

33. Typical “Double hump”
Carefully look for artifacts or
anatomical variations
Zone - 6 : RNFLTHICKNESS
TSNIT PLOT

34. Pie graph summery of TSNIT plot
Avg RNFL thickness
Inf: 120 micro m
Sup: 112 micro m
Nasal: 72 micro m
Temporal: 70 micro m
Zone-7 : RNFLQuadrant &
RNFLClock-hour thickness
measurement

35. To check the correct localization of the
BMO (black), which define the limits of
the ONH and on the projections on to
the surface of the internal limiting
membrane (red) to determine the edge
of the NRR
To identify artifact related to NRR
Zone-8 : Extracted vertical &
horizontal tomogram

36. Zone-9 : RNFLcircular tomogram
 To look for
Artifacts
Segmentation errors
Retinal diseases that can
cause green disease

38. OCT
OF
MACULAR GANGLION CELLS
• The macula is densely populated by RGCs, containing 50%
of the total number of these cells while occupying only
2% of the retina’s area.
• GCL comprises 30-35% of total macular thickness
• Loss of RGC'sin early glaucoma is more likely to occur
in macula

39. OCT
OF
MACULAR GANGLION CELLS
• GCC composed of
• Innermost retinal layers
• RNFL + GCL + IPL
• Zeiss’ Cirrus HD-OCT
• GCL+IPL

40. OCT
OF
MACULAR GANGLION CELLS

41. OCT
OF
MACULAR GANGLION CELLS
Zone-1 : Pt. I.D & Signal strength
Zone-2 : Thickness map
Zone-3 : Deviation map
Zone- 4 : Sector map
Zone- 5 : Thickness table (Avg thickness: 75 micro m)
Zone- 6 : Macular Horizontal Tomogram

42. 2

43. OCT Panomap Analysis : Right Eye
Combination of
 200 × 200 Optic Disc
Cube and
 512 × 128 Macular Cube
scans
 Macular full thickness map

44. Normative database
of
OCT Glaucoma Protocol
1) 284 healthy adults
2) Age range of 18–84 years
3) Refractive error of −12 to + 8D/ +6 D
4) Ethnicity includes Caucasians 43%, Asians 24%, African
America 18%, Hispanic 12%, mixed ethnicity 6% and Indian 1%.
5) Disc area is < 1.3 mm2 or > 2.5 mm2 rim area
6) Vertical C:D >2.5

45. LIMITATIONS OF OCT
 Limited applications in poor media clarity
 Corneal edema
 Dense cataracts
 Vitreous hemorrhage
 Asteroid hyalosis
 High astigmatism and decentered IOL may compromise the
quality

46. Next class
Clinical co-relation
And
Artifacts